Single longitudinal mode ring Raman laser

A single longitudinal mode ring Raman laser including:

• a pump source outputting a pump light power, mode matched and resonantly coupled to a ring resonator;
• the ring resonator including a Raman gain medium;
• wherein the Raman gain medium receives the pump light power and undergoes Raman lasing generating Stokes power at a corresponding Stokes wavelength;
• the ring resonator acting as laser feedback loop for the pump light power and the Stokes power and outputting a portion of the Stokes power as the laser output;
• and
• a unidirectional isolator for causing the Stokes output power to propagate in one direction within the ring resonator;
• wherein the unidirectional isolator includes a partially reflective element, or an element with second order nonlinearity to provide sum frequency mixing of the pump light power with the Stokes power to force unidirectional backwards Stokes oscillation with respect to the pump light power.